Hollow inflatable formwork elements for producing concrete structures

ABSTRACT

The present invention relates to reusable hollow formwork elements of elastic material which may be used for the concreting of pipelines, and which by filling with a gaseous or liquid medium, can be given compressive resistance. The invention also relates to a method of operating such formwork elements.

United States Patent Friedi 1 1 Aug. 12, 1975 HOLLOW INFLATABLE FORMWORK1,964,386 6/1934 N656 249/65 ELENIENTS FOR PRODUCING CONCRETE 2,485,89810/1949 Mathews 6! al 249/65 2,579,423 12/1951 Ford 249/65 STRUCTURES3,104,441 9/1963 Smith 249/65 [75] Inventor: Franz Friedl, Vienna,Austria .3 5 1/19 aas 5 X 0 3,648,963 3 1972 Smith 249/65 [73] Ass1gnee:Sempent Aktiengesellschaft, Austria Filedi J 1973 PrimaryExaminerFrancis S. Husar [2]] App. NO: 323 355 Assistant ExaminerJohnMcQuade Attorney, Agent, or Firm-Ernest F. Marmorek [30] ForeignApplication Priority Data Jan. 13, 1972 Austria 253 72 [57] ABSTRACT Thepresent invention relates to reusable hollow form- [52] US. Cl; 249/65;249/178 work elements of elastic material which may be used [51] Il'lt.Cl. 828B f th r ting of pipelines, and which by [58] held of Search249/65, 178 with a gaseous or liquid medium, can be given pressiveresistance. The invention also relates to a [56] References C'ted methodof operating such formwork elements.

UNITED STATES PATENTS 1,600,353 9/1926 Nose 249/65 x 3 7 Draw'ng F'gures1 1 30 .70 f 25 a; I J 24 v I\ 1 24 I 4/ A i 23 0 PATENTED AUG 1 2 I975SHEET HOLLOW INFLATABLE FORMWORK ELEMENTS FOR PRODUCING CONCRETESTRUCTURES BACKGROUND OF THE INVENTION By way of formwork material forconcreting purposes, wood, sheet metal and, more recently, flexiblematerials such as synthetic plastics material sheets or foamed syntheticmaterials, have been used. In order, however, to be able to use aflexible formwork skin, it is necessary to maintain the desired forworkshape by using internal spacers of suitable material. By theincorporation of spacers, however, so-called lost formwork, i.e. thesynthetic plastics material formwork remains in situ in the concretedcomponents.

On the other hand, so-called telescopic formwork arrangements of steelor light alloy are known, which are used in tunnelling work and consistof a multipart formwork system arranged on a mobile assembly. The use ofthis kind of system makes it possible to build a tunnel lining in acontinuous manner. The use of formwork sections of this kind or formworkelements which do not have a uniform, smooth surface, necessitatesconsiderable subsequent work because the concrete surface has to havethe flash witnesses removed from it. The use of formwork removal agentswhich are applied to the formwork before the concreting operations arecommenced, although ensuring trouble-free removal of the formworknevertheless means that subsequent treatment of the surface, at least atthe points of connection, is essential.

Also known are tubelike or sacklike formwork arrangements for theconcreting of ceilings and particularly for reinforced concrete ribbedceilings, these arrangements being made of a slack, flexible materialsuch as rubber tubing or sacking. Tubes of this kind can be operated byfilling them with air, water or sand and providing a closable insert.

The tubes consist of a sheet of synthetic plastics material as theenvelope with tensile tensioning inserts and stiffening inserts whichare applied to fixing points and in this fashion ensure that a specificcross-sectional shape is maintained. Even under conditions ofintensivemaintenance, however, devices made of flexible material are subjected torelatively heavy wear because the tensioning inserts and reinforcinginserts make it very difficult to introduce the devices into positionand align them and it is extremely difficult to introduce the devicesinto position and align them and it is extremely difficult to re-usesuch hollow formwork elements. A great deal of extra labour is thusinvolved and efforts have therefore been made to use hollow elements ofcheap material in order to use them at lost formwork. Quite apart fromthis, however, the compressive resistance of this kind of tube ofsynthetic plastics material foil, is too low to justify regarding suchan element as a fullgrade piece of formwork.

Such hollow formwork elements made of elastic material may also be usedfor the manufacture of tubes or channels as is well known having across-section approximating that of an egg. This is conventionallyachieved by providing a cylinder of a larger diameter and anothercylinder of a smaller diameter which are interconnected along asuperficies line. In this case the,

connecting bridges, which extend tangentially as viewed in across-section, form an oval.

Assuming now that in the gusset formed by the two cylindrical walls onthe one hand and the connecting bridge on the other hand, there exists apressure which is too low, then the connecting bridge is pressed inwardsor alternatively an undesired concrete wedge is formed at the base orbottom plate. On the other hand if a higher pressure is selected whichavoids both of these disadvantages then an appreciable deviation fromthe oval form is caused by a bulging out of the connect ing bridgewithin the region of the bottom plate.

SUMMARY OF THE INVENTION An object of the invention is to overcome thedrawbacks of known hollow formwork elements and to provide a formworkelement of elastic material, which can be erected on site in its finalform, quite simply by filling it with a gaseous or fluid medium, andwhich can also be positioned very simply.

Another object of the present invention is to provide improved hollowformwork elements which may be used to cast pipelines having the desiredoval crosssection by simple means and which provide in greaterapproximation the desired cross-section of the pipeline.

The invention therefore consists in a reusable hollow formwork elementof elastic material, which element by filling it with a gaseous orliquid fluid medium can be given compressive resistance, comprising aformwork skin and internal walls attached thereto, said internal wallsforming at least three separate cavities extending over the full lengthof the formwork element and the hollow element formed by the skin beingclosed at its ends by covers fitted with fluid valves.

One or more of the cavities can be arranged to have a circularcross-section in the filled state. Alternatively, the cavities may havea prismatical cross-section instead of a circular cross-section.

Preferably, the diameters of two cavities which are circular in thefilled state are in the ratio of approximately 1:2. It has also beenfound convenient to attach the internal walls forming the cavities toone another over the full length of the formwork element at the commontangent or chord, with the cavities communicating with one anotherthrough one or more openings so that selected cavities can be filledwith fluid medium through a common valve.

In order to cast tubes of oval cross-section another embodiment of thehollow formwork elements of the invention may be used. In this case oneof the cylindrical, hollow spaces has such a diameter that it touchestangentially the two upper edges of the bottom plate. It has also beenfound to be suitable that if at least two of the hollow spaces in thefilled or inflated state have the shape of hollow cylinders from each ofwhich a segment of equal cord length has been cut away and which areconnected to each other along the section plane. In order to obtain anoval cross-section of the hollow framework element in the inflatedstate, it is preferred to provide one hollow cylinder with a diameterwhich may, for example, be approximately 20% larger than that of theother adjacent hollow cylinder. Furthermore, it has been found suitablefor concreting pipelines which have an oval cross-section and byutilizing a gutter-like bottom plate when the two hollow spaces areinterconnected by at least one opening of the inner wall disposed in thesection plane.

From another aspect the invention consists in a method of operating thehollow formwork element wherein selected combinations of the cavitiesare filled with fluid medium independently of one another throughrespective valves, the formwork skin being made to adopt the requiredprofile by adjusting the pressure in the cavities. To achieve asubstantially elliptical or oval cross-section two cavities which have acircular cross-section in the filled state, are maintained at the samepressure, whilst the remaining cavity or cavities is or are maintainedat a lower pressure. For example, a pressure difference of between 0.1and 0.5 atm may be provided.

The hollow formwork element is preferably made from a fabric with anoil-resistant coating e.g. a cotton fabric or a polyester fibre fabricwith a coating of a butadiene-acrylonitrile copolymer or a layer ofpoly-2- chlorobutadiene (Neoprene). Thus, normaly rubberized fabricswhich are designed for engineering applications, can be used. Theformwork skin must be made of oil-resistant material because it isessential to use formwork release agent based upon lubricating oils inorder to prevent the concrete from adhering to the formwork.

This kind of formwork element can, for example, be manufactured asfollows:

First, two cylinders closed at their ends, are manufactured fromrubberized fabric and attached to one another by bonding, whereafterthey are covered by an envelope wall which serves as a formwork skin.The open hollow element obtained in this way is then closed off at itsends by dish-shaped covers, each of which contains a valve.

The application of re-usable hollow formwork elements is indicatedwherever the in situ building of concrete pipes is required. Theformwork in accordance with the invention can be used to build pipelinesof all kinds, including curved ones. It is possible to produce differentprofiles using one and the same element, merely by altering and adaptingthe pressures in the cavities provided. The profile can be varied inthis context from the elliptical to the circular. With an element ofthis kind it is possible without particular difficulties, to carry outimprovement works, the element being placed in a pipe which is to beimproved and concrete introduced into the interspace formed between theenvelope wall of the element and the pipe.

Using a formwork element in accordance with the invention it is evenpossible to take account of changes in profile during the manufacture ofa pipeline. These elements are particularly suitable for application atpoints where access is difficult and space restricted.

In building concrete pipelines using a formwork element in accordancewith the invention, it is first of all necessary to provide a suitablebase or foundation. For example such a base or foundation ispreliminarily produced by concreting or a substrate suitable to performthis function is laid down. Then external formwork and possiblyreinforcing is introduced. The hollow formwork element is then insertedand inflated using compressed air and built-in pressure-reducer valvesmay be provided to ensure that the correct pressure is established. Inthis context, in order to achieve an elliptical or oval cross-section,of the kind often required in ducting, the pressure ratio is socontrived, that the two circular tubes are maintained at the samepressure whilst the remaining cavity is inflated to a lower pressure.

During the concreting operation, the hollow element is held down at thetop to prevent it floating off. After the concret has cured, thecompressed air is blown off from the hollow form-work element and theelement, which then lies slack in the finished pipeline, can bewithdrawn. It is possible too, of course, simply to blow off a smallquantity of air and to shift the element onwards by a distancecorresponding to the concreted length of pipe.

BRIEF DESCRIPTION OF THE DRAWINGS Exemplary embodiments of the inventionwill now be described with reference to the drawings forming part ofthis Specification, in which:

FIGS. 1 and 2 show a hollow formwork element in a perspective view andin section along the longitudinal axis,

FIGS. 3 to 5 show further embodiments of the hollow formwork in section,

FIG. 6 is a cross-sectional view ofa pipeline with eggshaped profile andhaving a known hollow formwork element, the figure being divided by avertical, symetrical line into two portions, and

FIG. 7 is a cross-sectional view of such a pipeline provided with ahollow formwork element in accordance with the present invention, thefigure being again divided by a vertical, symetrical line into twoportions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, ahollow formwork element comprises two elongated tubes 6 and 8 which inthe filled or inflated state have an approximately circular crosssectionand whose diameters are approximately in the ratio 1:2. The two tubesare attached to one another along the line 12 and transfer orifices 13for the filling medium, are provided therebetween. The two tubes aresurrounded by a formwork skin 1 of rubberized fabric having a tearingstrength of around 320 kg per square centimeter. The tubes 6 and 8 areprovided at their ends, as shown in FIG. 2, with caps 4 to close themoff. One of these caps contains a common filling and blowoff valve 9 forboth tubes. The filling medium, e.g. compressed air, passes unimpededlythrough the openings 13 from one tube to the other. The intermediatespace, or spaces 7 which are formed between the formwork skin 1 and thetubes 6 and 8, is or are inflated or filled through the valve 10. Thevalve 10, as FIG. 2 shows, is contained in one of the two end covers 20of the formwork skin 1. Consequently, the cavity 7 between the tubes 6and 8 and the formwork skin 1 is filled with the pressurized medium.

In the embodiment shown in FIG. 3, three tubular elements 17 of the samediameter, are arranged one above the other. FIG. 4 on the other hand,shows a substantially elliptical hollow formwork element comprising acentral tubular element 19 with a diameter at most equal to the minoraxis of the desired elipse to which two tubular elements 18 of smallerdiameter are attached.

FIG. 5 shows a further embodiment of a hollow formwork element inaccordance with the invention in operation. Set up on a pre-concretedfoundation 21, there is shown an approximately elliptical hollowformwork element comprising a formwork skin 1. The internal wall parts 2and 3 do not themselves define closed cavities but are attached to theformwork skin 1 along lines 15 and 16 to form corresponding cavities 6,7 and 8, and between these two attachment lines 15 and 16, the formworkskin 1 is reinforced by a reinforcing insert 14. After the placing ofthe hollowformworkelement on the pre-concreted foundation",1 the twotubes '6 and 8 which can be commonlyinflatedby-a valve 9,-are inflatedwith compressed air to around l.;375;,atm,,whilst the remaining cavity7, between the formwork skin 1 and the two tubes 6 and 8, is inflatedthrough the valve 10 to about 1.1 atm. formwork with an approximatelyoval cross-section is thusproduced. The hollow formwork element issubsequently surrounded with concrete in the desired fashion and left inthe cavity thus formed, until the concrete is cured. 'Then, the pressurein the two elongated tubes of circular crosssection is reduced slightlyso that the hollow formwork element lifts away from the innerjwall ofthe pipe which has been thus formed and can be moved longitudinally forfurther use.

Referring now to FIG. 6, there is showna chaiiriel 22 within which thereare disposed again two superimposed, elongated tubes or hoses 6 and 8. Aprefabricated base or bottom plate'23 extends with its ends 24 beyondthe lower elongated tube 6. The elongated sired line 35.

On the other hand, if a lower inflating pressure is selected asillustrated in FIG. 6 on the right-hand side at b, there is also adeviation 1" of the formwork skin 1 from the prescribed line 35. This isprimarily caused by the fact that concrete enters between the skin 1 andthe bottom plate 23.

In order to obtain the desired oval cross-section of the channel theshape of the inflatable, hollow element of elastic material is selectedin accordance with the present invention as illustrated in FIG. 7. Thehollow element is provided, as illustrated, to the left of the verticalsymmetry plane at a with an outer formwork skin 1. The skin 1 is closedupon itself to form an elongated tube and is of such size whichcorresponds in the inflated state to the desired cross-section of thecanal and which also touches the prefabricated bottom plate 23 of thecanal. The hollow element is further provided with two innerstrip-shaped portions 25 and 26 which are adjacent to the surfaces 25and 26 and which are connected with each other at least at theborderline 32 of these surfaces. By means of these portions 25 and 26the egg shape is maintained. In the middle of the two surfaces 25' and26' disposed adjacent to each other there is provided at least onecorresponding opening 27 which serves the purpose to connect with eachother the two spaces for the purpose of inflating them.

The diameter of the upper hollow space 29 is approximately larger thanthe diameter of the lower hollow space 28. The latter has such adiameter that in its inflated state it touches tangentially the twoupper ends 24 of the bottom plate 23.

As previously described, at one of the walls disposed at the two ends ofthe elongated hollow body, there is provided a valve 31 by means ofwhich air may be forced into the hollow spaces 28 and 29. In order toinflate the two gussets 30 which are formed at the side walls of thetube-like hollow spaces 28 and 29, it is also required that a fillingvalve be provided at one of the end walls of the formwork skin 1.

It is also feasible in accordance with the present invention to arrangethe hollow formwork element as shown on the right-hand side of thesymmetry plane shown at b. In this case elongated closed hollow flexiblebodies or tube-like portions 33 and 34 are disposed within the formworkskin 1. These parts again meet each other at the surfaces 33' and 34'and are at least connected with each other along the borderline 32. Inthis case also a gusset 30' is formed. This results, when the hollowformwork elements are inflated, in the hollow formwork elements havingthe shape of hollow cylinders with equal cord length segments cut awaywhereby the hollow cylinders may be connected at a section plane.

I claim:

1. A re-usable hollow formwork element, for use in concrete pipe castingand operable to be rendered pressure resistant by filling it with afluid medium,

comprising in combination,

an elongated, inflatable flexible closed outer casing of predeterminedshape when inflated,

at least two elongated adjacent superposed closed hollow flexible bodiespositioned along a substantially vertical axis whereby one hollowflexible body is positioned lower than all other hollow flexible bodies,within, and extending over the entire length of, said outer casing,whereby an elongated closed cavity is formed intermediate said outercasing and said bodies, said bodies as well as said cavity beingoperative to be pressurized by said fluid medium,

each of said hollow bodies having at least one portion facing therespective portion of the adjoining body, and each defining an openingin said portion, the adjoining bodies intercommunicating interiorlythrough said openings,

a first valve connected to one body operable for introducing said fluidmedium thereinto for pressurizing thereby both said bodies to inflatethem,

a second valve connected to said outer casing adjacent said elongatedcavity, operable for introducing said fluid medium into said elongatedcavity for pressurizing thereby said cavity, whereby the outer casingwill be inflated to its predetermined shape, and

support means operable for supporting the casing when inflated where thelower of said bodies touches said casing, said support means stoppingshort of said elongated cavity and including a gutter-like bottomplatehaving two ends at an angle to each other,

a part of said casing adjacent said one hollow flexible body beingdisposed above said bottom plate and when inflated having an externalarcuate surface touching tangentially said ends of said bottom platewhen inflated, whereby said inflated casing will be supportedsubstantially only by said ends.

2. A re-usable hollow formwork element, for use in concrete pipe castingand operable to be rendered pressure resistant by filling it with afluid medium,

comprising in combination,

an elongated, inflatable flexible closed outer casing of predeterminedshape when inflated,

at least two elongated adjacent superposed closed hollow flexible bodiespositioned along a substantially vertical axis whereby one hollowflexible body is positioned lower than all other hollow flexible bodies,within, and extending over the entire length of, said outer casing,whereby an elongated closed cavity is formed intermediate said outercasing and said bodies, said bodies as well as said cavity beingoperative to be pressurized by said fluid medium.

each of said hollow bodies having at least one portion facing therespective portion of the adjoining body, and each defining an openingin said portion, the adjoining bodies intercommunicating interiorlythrough said openings,

wherein at least two of said bodies have the shape of hollow cylinderswhen inflated, a segment of each of said hollow cylinders being cut awayto form a section plane, said segments having equal cord lengths, andsaid cylinders being connected with each other at the section plane,

a first valve connected to one body operable for introducing said fluidmedium thereinto for pressurizing thereby both said bodies to inflatethem,

a second valve connected to said outer casing adjacent said elongatedcavity, operable for introducing said fluid medium into said elongatedcavity for pressurizing thereby said cavity, whereby the outer casingwill be inflated to its predetermined shape, and

support means operable for supporting the casing when inflated where thelower of said bodies touches said casing, said support means stoppingshort of said elongated cavity.

,3. A formwork element as claimed in claim 2,

1. A re-usable hollow formwork element, for use in concrete pipe castingand operable to be rendered pressure resistant by filling it with afluid medium, comprising in combination, an elongated, inflatableflexible closed outer casing of predetermined shape when inflated, atleast two elongated adjacent superposed closed hollow flexible bodiespositioned along a substantially vertical axis whereby one hollowflexible body is positioned lower than all other hollow flexible bodies,within, and extending over the entire length of, said outer casing,whereby an elongated closed cavity is formed intermediate said outercasing and said bodies, said bodies as well as said cavity beingoperative to be pressurized by said fluid medium, each of said hollowbodies having at least one portion facing the respective portion of theadjoining body, and each defining an opening in said portion, theadjoining bodies intercommunicating interiorly through said openings, afirst valve connected to one body operable for introducing said fluidmedium thereinto for pressurizing thereby both said bodies to inflatethem, a second valve connected to said outer casing adjacent saidelongated cavity, operable for introducing said fluid medium into saidelongated cavity for pressurizing thereby said cavity, whereby the outercasing will be inflated to its predetermined shape, and support meansoperable for supporting the casing when inflated where the lower of saidbodies touches said casing, said support means stopping short of saidelongated cavity and including a gutter-like bottom plate having twoends at an angle to each other, a part of said casing adjacent said onehollow flexible body being disposed above said bottom plate and wheninflated having an external arcuate surface touching tangentially saidends of said bottom plate when inflated, whereby said inflated casingwill be supported substantially only by said ends.
 2. A re-usable hollowformwork element, for use in concrete pipe casting and operable to berendered pressure resistant by filling it with a fluid medium,comprising in combination, an elongated, inflatable flexible closedouter casing of predetermined shape when inflated, at least twoelongated adjacent superposed closed hollow flexible bodies positionedalong a substantially vertical axis whereby one hollow flexible body ispositioned lower than all other hollow flexible bodies, within, andextending over the entire length of, said outer casing, whereby anelongated closed cavity is formed intermediate said outer casing andsaid bodies, said bodies as well as said cavity being operative to bepressurized by said fluid medium, each of said hollow bodies having atleast one portion facing the respective portion of the adjoining body,and each defining an opening in said portion, the adjoining bodiesintercommunicating interiorly through said openings, wherein at leasttwo of said bodies have the shape of hollow cylinders when inflated, asegment of each of said hollow cylinders being cut away to form asection plane, said segments having equal cord lengths, and saidcylinders being connected with each other at the section plane, a firstvalve connected to one body operable for introducing said fluid mediumthereinto for pressurizing thereby both said bodies to inflate them, asecond valve connected to said outer casing adjacent said elongatedcavity, operable for introducing said fluid medium into said elongatedcavity for pressurizing thereby said cavity, whereby the outer casingwill be inflated to its predetermined shape, and support means operablefor supporting the casing when inflated where the lower of said bodiestouches said casing, said support means stopping short of said elongatedcavity.
 3. A formwork element as claimed in claim 2, wherein saidcylinders are connected to one another over the full length of theformwork element at the section plane.